Linear polyolefins made using a mono-functional initiator containing a single “exo-olefin”, “1,1-di-substituted” olefin, or “methylvinylidene,” end group are useful precursors for the preparation of polymers containing specific functional end groups. Polymers made using multi-functional initiators would have multiple exo-olefinic end groups. Polymers containing specific end groups are useful as lubricating oil additives. One example of a functionalized polymer containing hetero atoms is polyisobutenylsuccinic anhydride, which is produced by reaction of olefin terminated polyisobutylene with maleic anhydride. Functional end groups may also be desirable for synthesizing polymers capable of undergoing further reaction.
Conventional ionic polymerizations can be anionic or cationic. Anionic polymerizations proceed, in the presence of a base, through carbanions and favor monomers having electron withdrawing groups. Cationic polymerizations proceed, in the presence of an acid, through a carbocation, also called a carbenium ion, and favor monomers that have electron releasing groups.
Similarly to the conventional polymerization systems, living polymerization systems may be either anionic or cationic. The difference between conventional polymerizations and living polymerizations is that an ideal living polymerization proceeds in the absence of chain transfer and chain termination. Living polymerization systems are of great commercial importance because the degree of polymerization may be controlled by controlling the feed ratio of monomer to initiator and sequential addition of two or more different monomers affords the ability to produce block copolymers. Polymerization continues until the monomer is exhausted, but the polymers retain their ability to add additional monomers any time in the future. A number of such systems are well known in the art.
A further development is the cationic quasi-living polymerization systems using conventional monomers. Quasi-living polymerization is best achieved when certain conditions are employed, for example anhydrous reagents. Cationic quasi-living polymerizations differ from truly living polymerizations in that, although the rate of chain transfer approaches zero, chain termination is present but reversible. One important example of a cationic quasi-living polymerization is the cationic quasi-living polymerization of isobutylene.
Typically, cationic quasi-living polymerizations of isobutylene yield narrow molecular weight distribution and one major polymer product containing the 2-chloro-2-methylpropyl end group, also referred to as the “tert-chloride” end group. Under certain conditions minor amounts of olefinic isomers may also be produced. On the other hand, there are two major olefinic isomers produced during conventional polymerization of isobutylene with BF3. The highly reactive exo-olefin isomer is the most abundant and the relatively unreactive 2-methyl-1-propenyl isomer is also produced. The 2-methyl-1-propenyl isomer is also referred to as the “tri-substituted” isomer or “endo olefin” isomer. Furthermore, conventional polymerization of isobutylene yield polymers with broader molecular weight distributions or polydispersity indices than typical quasiliving polymerizations.
Exclusive production of the exo-olefin isomer has not been previously achieved under conventional polymerization conditions.
There are two established methods for producing polyisobutylene containing only the exo-olefin end group. One method involves chemical dehydrohalogenation of tert-chloride terminated polyisobutylene using potassium tert-butoxide in a post polymerization reaction (U.S. Pat. No. 4,342,849). The other method involves in situ quenching of quasi-living isobutylene with methallyltrimethylsilane, which converts an active, living carbenium ion to the exo-olefin end group. See for example, Roth and H. Mayr, Macromolecules, 29, 6104, 1996; and Nielsen, L. V.; Nielsen, R. R.; Gao, B.; Kops, J.; Ivan, B. Polymer 1997, 38(10), 2529.
Polyisobutylene polymers containing more than one exo-olefin end group may be prepared using the above methods by the use of a multi-functional initiator. The preparation of polyolefins, including polyisobutylene polymers, is well known in the art. A number of patents have discussed processes for making polyisobutylene polymers containing exo-olefin end groups, but none using quenching a cationic quasi-living polymerization system with the substituted azole compounds of the present invention.